1. Field of the Invention
The present invention relates to a recording apparatus that can perform high quality image recording. Recording performed by the present invention involves the application of ink to ink supports, such as cloth, paper, and sheet material. The present invention is applicable both to various data processing apparatuses and to printers that serve as output devices that perform the above recording.
2. Related Background Art
As personal computers, word processors, and facsimiles are widely used in offices, various types of recording apparatuses have been developed as output devices for them. Recording apparatuses that employ the ink jet system are especially widely used because they are compact and produce less noise while recording.
Recently, high recording quality has also begun to be required for recording apparatuses for personal use. The recording quality is determined by such factors as image density, density irregularities, and the sharpness of images. The reason is as follows.
In an ink jet recording apparatus, a recording head has a plurality of ink nozzles in perpendicular to a direction of feeding a recording medium, and ink ejects perpendicular to the face of a recording medium.
The ink ejection direction is supposed to be identical for all the nozzles, but in actuality, the directions from the nozzles may vary. FIG. 22 is a specific diagram for explaining the occurrence of a fuzzy image due to a variation in the direction ink is ejected from a recording head, which is employed in an ink jet recording apparatus. FIG. 23 is a specific diagram for explaining the occurrence of a fuzzy image due to different ink ejection speeds. For example, as is shown in FIG. 22, although ink should originally be ejected in the direction indicated by the dotted arrow A, the nozzles that emit ink face in the direction indicated by the solid line arrow B. When the interval between an ink ejection face 300a of a recording head 300 and a recording medium 301 is D1, the actual ink discharge point Q is shifted from the original ink discharge point P by a distance represented by the interval L1. This shift reduces image sharpness and degrades the recording quality. When the interval between the ink ejecting face 300a and the recording medium 301 is D2, for example, the shift is increased from L1 to L2 (L1&lt;L2).
Besides the variance in the directions ink is ejected from the nozzles, differences in the speeds at which ink is ejected cause the fuzzy images. For example, ink droplets that are discharged from the nozzles are called main droplets, satellites, and micro dots, in order of size from the greatest. The ejection speeds for these ink droplets differ. Therefore, as is shown in FIG. 23, with the combination comprising the ink ejection speed V1 and the moving speed element VH for the recording head 300, ink is ejected in the direction indicated by the solid line arrow C; while with the combination comprising ink ejection speed V2 (V1&lt;V1) and the moving speed element VH, ink is ejected in the direction indicated by the dotted line arrow D. The ink discharge directions are different and the sharpness of an image is deteriorated. The shift increases as the interval between the ink ejection face 300a and the recording medium 301 increases.
To improve the recording quality, it is demanded that an ink jet recording apparatus maintain a constant minimum interval between an ink ejection face and a recording medium.
In response to such a request, a conventional ink jet recording apparatus employs a recording medium pressing means for forcing down a recording medium so as to maintain the interval between the ink ejection face and the surface of the recording medium.
However, when the recording medium pressing means is separated from the recording medium at the time a recording medium jam occurs, or during the feeding of a continuous recording medium, the recording medium pressing means must provide a greater interval between the ink ejection face and the recording medium.
The arrangement of a conventional ink jet recording apparatus will now be explained in further detail while referring to FIGS. 24, 25A and 25B.
FIG. 24 is a perspective view illustrating the structure of a conventional ink jet recording apparatus, and FIGS. 25A and 25B are side views of a paper pressing mechanism of the conventional recording apparatus. In FIG. 24, an external cover C1 and an internal cover C2 are either opened or removed. In this recording apparatus, the recording medium 301, such as a normal sheet or a plastic sheet, is inserted through an insertion port 302, a motor (not shown) rotates a feeding roller 303, and the sheet is guided by paper pressing plates 304, which are the recording medium pressing means, and is fed toward a recording position. The recording head 300, which is a serial print type recording means, is mounted on a carriage 305. The carriage 305 engages a lead screw 306, and as the lead screw 306 rotates the carriage 305 reciprocates in the directions indicated by the arrow a in FIG. 24. The directions indicated by the arrow a are perpendicular to the direction in which the recording medium is fed.
In synchronization with the reciprocal movement of the carriage 305, the recording apparatus 300 on the carriage 305 moves in consonance with an image signal and discharges ink to the recording medium 301 to perform predetermined recording.
The structure and function of the paper pressing plates 304 that prevents the recording medium 301 from separating from the surface of the feeding roller 303 will now be described.
As is shown in schematic diagrams in FIGS. 25A and 25B, each of the paper pressing plates 304 is formed with an almost cylindrical bearing 304a, and a long arm 304b and a short arm 304c, both of which extend from part of the bearing 304a. A pinch roller 307 is rotatably attached to the distal end of the arm 304b. A release shaft 308 is rotatably provided in the bearing 304a. The arc portions of the release shaft 308 are regularly cut off longitudinally at predetermined intervals and the notched portions have D-shaped cross sections. One end 309a of a pressure spring 309 can abut upon the notched portion and the arched portion of the release shaft 308, or the short arm 304c of the paper pressing plate 304. The other end of the pressure spring 309 is fixed to the bottom of a chassis 310.
As is shown in FIG. 25A, when the release shaft 308 rotates and the end 309a of the pressure spring 309 contacts the notch of the release shaft 308, the rotation of the release shaft 308 is halted and the short arm 304c of the paper pressing plate 304 is forced by the pressure spring 309 in the direction indicated by the arrow b. The paper pressing plate 304 is rotated on the release shaft 308 and the pinch roller 307 presses against the surface of the feeding roller 303. As the feeding roller 303 is rotated, the pinch roller 307 is rotated in the direction opposite to that of the feeding roller 303.
When the release shaft 308 is rotated further and the end 309a of the pressure spring 309 contacts the arc of the release shaft 308, as is shown in FIG. 25B, the pressure spring 309 is pushed down in the direction indicated by the arrow c and the force exerted on the short arm 304c of the paper pressing plate 304 by the pressure spring 309 is released, so that the pinch roller 307 is separated from the surface of the feeding roller 303.
The separation of the paper pressing plate 304 from the feeding roller 303, i.e., the release of the pressure exerted by the pressure spring 309, can be performed as needed by manipulating a release lever 311 shown in FIG. 24 to rotate the release shaft 308.
In the above described embodiment, however, when the paper pressing plate 304 is released from the feeding roller 303 by manipulating the release lever 311, the paper pressing plate 304 is positioned closer to the recording head 300, as is shown in FIG. 25B, and the paper pressing plate 304 interferes with the approach of the recording head 300 to the recording head 301.
In the modern information society, a variety of recording media are supplied that cannot simply be classified only as normal paper, fanfold paper, and postcards. In addition to those, there are plastic sheet material, such as OHP film, cloth, threads, and a variety of other various ink support media on which ink is applied and that are supplied as recording media.
A recording apparatus example that can feed this plurality of recording medium types is disclosed in the specifications for U.S. Pat. No. 5,158,380.
The arrangement of the disclosed recording apparatus will now be described while referring to FIGS. 26A and 26B.
FIGS. 26A and 26B are cross sectional views for explaining the state when a cut sheet supply mode is selected, and FIG. 26B is a cross sectional view for explaining the state when a continuous sheet supply mode is selected.
In FIG. 26A, single sheets of paper 401 are supplied either from the bottom or the top of the apparatus. For paper supplied from the bottom of the apparatus, a cut sheet 401 is fed through a paper supply port 404 that is formed by a guide roller 407 and a friction roller 408. The friction roller 408 is held against a pressure spring 424 by a hub 423, one end 424a of the pressure spring 424 is driven by a cam 419 on a release shaft 421 to forcibly press the friction roller 408 against the guide roller 407. The cut sheet 401 that is held by the friction roller 408 and the guide roller 407 is fed to a recording position 414 in consonance with the rotation of the guide roller 407, and recording is performed on the cut sheet 401 by a recording head 415.
To supply the cut sheet 401 from the top of the apparatus, it is fed through a paper supply port 404 that is formed by the guide roller 407 and a friction roller 409. The friction roller 409 is supported by a bearing 425 that rides on a plurality of leaf springs 426. One end 426a of each of the leaf springs 426 is supported by a support plate 427 and the other end 426b is supported by a cam 420 on a release shaft 422 so as to exert sufficient force to press the friction roller 409 against the guide roller 407. The cut sheet 401 that is held between the friction roller 409 and the guide roller 407 is fed to the paper supply port 404, in consonance with the rotation of the guide roller 407, and is then fed to the recording position 414, in the same manner as is performed for the above described bottom paper supply, and recording is performed by the recording head 415.
In FIG. 26B, continuous paper 2 is supplied via a paper supply port 406 by a push tractor 412 from the rear or the back of the apparatus. The release shafts 421 and 422 are respectively rotated in the directions indicated by the arrows, and the force exerted by the pressure spring 424 and the leaf spring 426 on the respective friction rollers 408 and 409 is released or decreased. Accordingly, a paper feeding failure due to the perforations on the continuous paper can be prevented.
In the above described embodiment, however, paper is supplied through the paper supply port 404 or 406, some recording media are fed while adhering to the guide roller 407 while other recording media are fed along a sheet guide 418a of a body frame 418. A print start position in a paper feeding direction therefore varies from recording medium to recording medium.
Further, when feeding a thick recording medium, such as a post card, the forward edge of the recording medium may abut upon the paper guide 418a and cause the recording roller 409 to slip, so that a sheet supply failure occurs. To overcome this shortcoming, the pressure with which the friction roller 409 is pressed against the guide roller 407 has to be increased, so that even though paper feeding is possible, a greater than normal load accelerates the wear of the bearing 425 of the friction roller 409 and decreases its useful life span.
In addition, the interval between the surface of a fed recording medium and the ejection face of an ink jet head must be determined while considering the distortion of the surface of the recording medium that may occur due to a phenomenon called cockling. Cockling is a phenomenon where ink permeates the fibers of paper, etc., and expands the fibers so that the surface of the recording medium is distorted and undulating.